1. Field of the Invention
The present invention relates to gas-impermeable sealer elements for pyrotechnic delay detonators and to methods of making such sealer elements. The sealer elements of the present invention comprise encapsulated reactive materials such as multilayer metal foils or wires or oxidation/reduction reaction pairs deposited on suitable substrates, or the like.
2. Description of Related Art
It is known that reactive metal foils may be utilized in a multilayered foil structure which, upon appropriate excitation, undergoes an exothermic chemical reaction to generate a significant amount of heat. U.S. Pat. No. 6,736,942, issued May 18, 2004 to T. E. Weihs et al., discloses (column 1, lines 34-44) that such multilayer foils may be used primarily as sources of highly localized (column 2, line 26 et seq.) heat for various purposes including ignition in virtually any environment including air, vacuum, water, etc. Other examples of such reactive multilayer foils are described in U.S. Pat. No. 6,863,992, issued Mar. 8, 2005 to Weihs et al. The entire disclosures of the two Weihs et al. patents are incorporated by reference herein.
Such reactive multilayer foils are fabricated by depositing onto a substrate multiple alternating thin layers of dissimilar materials, e.g., metals, by any suitable process. The dissimilar metals, e.g., nickel and aluminum, may be comprised of any materials which undergo self-sustaining exothermic reactions such as alloying of the metals, or other exothermic changes in chemical bonding, in response to being heated to an elevated (initiation) temperature. Atmospheric oxygen or other extraneous oxidizers are not required for such reactions, which are therefore referred to herein as “self-sustaining” reactions. Metallic multilayered foil laminates comprising hundreds of alternating, extremely thin layers of such dissimilar metals are commercially available from Reactive Nanotechnologies, Inc. of Hunt Valley, Md.
A product sold under the trademark PYROFUZE® is a wire manufactured by Sigmund Cohen Corp. of Mount Vernon, N.Y., and consisting of at least two metallic elements in intimate contact with each other, including arrangements of one metal as a sheath encasing the other metal, thereby providing a laminated reactive multilayer wire. A plurality of thin sheaths of alternating different reactive metals may overlie each other. As is the case with the multilayer foils, when the two metallic elements of the wire are brought to their initiation temperature, they alloy rapidly, resulting in an exothermic, rapid reaction without necessity of atmospheric oxygen or other extraneous oxidizer.
U.S. patent application publication US 2006/0236887 A1 of John Childs et al. for “Delay Units and Method of Making the Same” was published Oct. 26, 2006, and matured into U.S. Pat. No. 7,650,840 (“the '840 Patent”). The '840 Patent discloses a delay unit for detonators comprised of a timing strip 14 (FIG. 1) deposited on a substrate 12 and comprised of a reactive material which emits energy upon being heated to its initiation temperature. The energetic material, which may comprise explosive, pyrotechnic or other energy-emitting material such as a fuel and an oxidizer, may be applied to the substrate by ink compositions containing particles of the energetic material dispersed in a continuous liquid phase, and some or all of the energetic material particles may be nanosize particles. See the Abstract and col. 2, lines 43-55. The ink dries or cures to form a solid, agglomerated mass, i.e., a mass without loose particulate materials.
U.S. patent application Ser. No. 11/674,300, filed on Feb. 13, 2007, in the name of Tyson J. Plitt et al. and entitled “Delay Elements, Detonators Containing the Same and Methods of Making” (“the Plitt et al. Application”), now abandoned, discloses a delay element suitable for use in otherwise conventional detonators. The delay element comprises a substrate upon which is disposed a reactive material which may be a reactive multilayer laminate of at least two different materials, e.g., aluminum and nickel.
While the reactive materials of the '840 Patent and the Plitt et al. Application may be similar or identical to those utilized in the present invention, both the '840 Patent and the Plitt et al. Application require that the reactive material must be configured into a zig-zag, serpentine or coiled path, and/or multiple paths connected in series, in order to increase the effective travel path of the reaction and commensurately increase the time delay provided by the delay element. See, e.g., FIG. 1 of the '840 Patent and FIGS. 9 and 11 of the Plitt et al. Application.
In blasting systems, signal transmission lines, such as electrical wires, detonating cord, shock tube and the like serve as energy sources to transmit an electric or non-electric energetic initiation signal to detonators or other devices. As is well known in the art, it is often necessary to attain precisely controlled delays between receipt of the initiation signal by the detonator and initiation of the output charge of the detonator in order to effectuate the desired timing of sequential detonations in a given shot, which may contain hundreds of detonators. Typical delay periods range from 9 to 9,600 milliseconds or more, for example, 9, 25, 350, 500 and 1,000 milliseconds. In order to attain such delays, conventional pyrotechnic delay elements are disposed within the detonator between the energy source, i.e., the signal transmission line, and the output charge.
U.S. Pat. No. 5,031,538 (“the '538 Patent”) discusses the problem of variations in the functioning time of pyrotechnic delay units, or failure of such delay units, citing a number of different reasons, including variations in pressure within the detonator. See the Abstract and column 1, line 63 to column 2, line 37 of the '538 Patent. The '538 Patent attempts to address the problem by providing an ignition buffer 45 (FIGS. 1 and 2) and also discloses the use of a “transition element 26” (FIG. 1) which is used to insure transmission of the input signal from the shock tube to the delay element. The transition element 26 is also intended to seal the delay element to provide a constant volume environment for burning of the delay element.